I think anything you might find that is intended to move people will be made with every possible safeguard to keep people from killing or dismembering themselves. you'll have safety cages, brakes systems, etc. if you don't need to move yourself (or don't mind going against the safety police, I would consider what someone earlier mentioned - an inexpensive harbor freight hoist. i picked up the 880 lb one clean-used at a used tool place for something like $45 a few years back that i use on my portable gantry. they're about $135 new i think. you could make an expanded metal platform that folds up like the one you showed, and if you pick it from all 4 corners when tipped down, you might be able to get away with something like old garage door tracks and rollers as vertical guides. the hoist will have the heavy load, they will just be to stabilize. Just gotta be able to secure the hoist and ensure the roof / wall you pull from will take the load. I'm sure the safety police will shut me down because there's a million ways to get hurt if you do stupid stuff.